gh-156774: Speed up pdb startup with asyncio guard - #156775
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brittanyrey wants to merge 3 commits into
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Defer the eight imports that are not already pulled in by pdb's required-eager imports (cmd, bdb, code, typing and the guarded _pyrepl.utils), and lift five unguarded function-level imports to module-scope lazy imports. Guard Pdb._get_asyncio_task() on 'asyncio' in sys.modules. It runs on every interaction(), so without the guard the deferred asyncio import is paid back immediately on the first breakpoint and the lazy import buys nothing for an actual debugging session. If asyncio was never imported there cannot be a running task, so returning None is equivalent. The guarded imports (readline, rlcompleter, _pyrepl) stay function-level: they sit in try/except ImportError blocks, and hoisting them would move the failure outside the guard. import pdb -42.1% breakpoint() -> cont -41.1% python -m pdb script -33.4% pdb post-mortem -33.3%
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See #156567 for the lazy imports, your review welcome! I was planning on doing the asyncio guard as a followup :) Shall we reduce this PR to just that? |
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Sorry about that! I did a peek over the lazy imports label & missed your issue! I'm glad to scope this down to just the asyncio gated change. |
brittanyrey
changed the title
Drop the other lazy imports and the lifted function-level imports, leaving just the asyncio deferral and the _get_asyncio_task() guard. Those two carry most of the win and keep the diff to five lines. import pdb -28.8% (was -42.1% with the full set) breakpoint() -> cont -28.5% python -m pdb script -26.0% pdb post-mortem -24.6%
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PR + issue are fully rescoped @hugovk |
johnslavik
approved these changes
Sep 1, 2026
hugovk
approved these changes
Sep 2, 2026
| import socket | ||
| import typing | ||
| import asyncio | ||
| lazy import asyncio |
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Let's also move this to after from warnings import deprecated: eager first, then lazy.
maurycy
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Sep 2, 2026
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| Speed up :mod:`pdb` startup by deferring the :mod:`asyncio` import, and by | ||
| skipping it entirely in ``Pdb._get_asyncio_task()`` when no event loop has | ||
| been used. |
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The news is for users. Maybe just:
Suggested change
| Speed up :mod:`pdb` startup by deferring the :mod:`asyncio` import, and by | |
| skipping it entirely in ``Pdb._get_asyncio_task()`` when no event loop has | |
| been used. | |
| Speed up :mod:`pdb` startup by only importing :mod:`asyncio` when the program | |
| being debugged has already imported it. |
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summary
perf
Broken out impact of lazy imports + asyncio guard
Without it, only the initial import really improves:
import pdbbreakpoint()→ continuepython -m pdb script